1. Field of the Invention
This invention relates to an inter-shaft journal assembly of a multi-spool turbo machine.
2. Summary of the Prior Art
As is known, for example from French patent application No. 80.13116, turbo machines of the multi-spool type include journal bearing means which support in rotation a first shaft with respect to a second shaft and this journal bearing means includes a roller bearing inserted between an internal ring mounted directly on the first shaft and an external ring mounted within a casing itself mounted on the second shaft. In the practical application of the assembly described in the specification referred to, the first shaft disposed internally is constituted by a shaft of the high-pressure spool shaft line and the second shaft, disposed externally, is constituted by a shaft of the low pressure spool shaft line.
In these journal bearings operative between the shafts, deflections of mechanical origin under the action of centrifugal force and deflections of thermal origin give rise to play or clearance, in particular radial play during running of which the consequences are harmful. Vibrations which shorten the life of the bearings may result. The construction disclosed in the application referred to above, by adopting an "inverted" configuration, in which the low-pressure shaft surrounds the high-pressure shaft and supports the outer race of a roller bearing of large diameter which is connected to a member of the structure of which the temperature and the rotational speed are lower, improves the longevity of the journal bearing means by reducing deflections liable to cause radial play or clearance.
Solutions for damping vibrations by an oil film have been also applied. However, in spite of these precautions, in modern turbo machines, in particular high power multi-flow turbo-jet engines, achievement of high performance and the use of large diameters renders these prior arrangements inadequate to avoid deflections and deformations of the high pressure shaft; further the generation in the roller bearings of excessive radial clearances are harmful to the service life of the journal bearings which in turn, if not replaced, are capable of adversely affecting the conditions of dynamic operation of the rotor and the aerodynamic-thermal performance of the turbo-machine.
An object of the present invention is to improve an inter-shaft assembly of a turbo-machine, so as to avoid these disadvantages.